The present invention relates to hermetic terminal assemblies and more particularly to a unique sealing structure for hermetic terminal assemblies.
Sealing members between the pin and walls of terminal assemblies have long been known in the art, particularly those of a type wherein a metallic cup-shaped body is utilized to cover and seal an opening in a hermetically sealed housing, the metallic cup-shaped body including at least one aperture with an annular lip extending therearound, the aperture serving to accommodate an electrically conductive metallic pin extending therethrough. A suitable fuse member has been associated with the electrically conductive pin and the pin has been sealed to the annular lip extending around the aperture in the cup-shaped body by a suitable sealing member such as glass. Several types of such glass-to-metal hermetic terminal assembly arrangements can be found in the art, such as in U.S. Pat. No. 4,580,003, issued on Apr. 1, 1986 to B. Bowsky et al, U.S. Pat. No. 4,584,433, issued on Apr. 22, 1986 to B. Bowsky et al and U.S. Pat. No. 5,017,740, issued to G. Honkomp et al on May 21, 1991. The art also has recognized that weakened hermetic seals have developed in the glass-to-metal sealing arrangements and has reduced occurrence of undesirable voids in the glass seal by controlling heating and glass flow in a preselected direction, attention being directed to U.S. Pat. No. 4,888,039, issued to B. Bowsky on Dec. 19, 1989, wherein an upwardly directed glass flow heating gradient has been utilized to flow glass sleeves forming sealing members around electrically conductive pins from bottom to top to firmly fuse the terminal pins with minimal voids in the glass sleeves. The present invention recognizes the importance of maintaining a proper durable sealing relation of a conductive pin in a hermetic terminal assembly structure not only in the formation of the conductive pin seal but also in the operation of such conductive pin seal under extraordinary stressful and heated conditions--such as during periods of extraordinary current swells which produce temperature rises to undesirable levels so as to cause associated fuse melting with concomitant electrical current interruption through the conductive pin. The present invention recognizes the importance of maintaining the integrity of the overall system to permit this preselected current interruption during excessive operation conditions and particularly the importance of maintaining the integrity of the pin sealing members during accompanying excessive heats. Recognizing the possibilities of sealing member melt occurrence prior to appropriate fuse functioning, the present invention resolves this problem in a straight-forward and economical manner by employing a unique sealing member which has preselected physical properties compatible with the materials with which it engages and preselectively compatible with conditions associated with fuse melting. To do this, the present invention recognizes and utilizes sealing materials which include chemical composition characteristics of a type generally known in the art and which in accordance with the present invention are employed to insure appropriate operational performance capability of fusing elements associated with electrical conductive pins during undesirable current surges with accompanying higher heat levels. In this regard, the present invention recognizes the unique value of employing sealing materials having high temperature melting characteristics, such high temperature melting glasses long known in the art and generally described in detail in such U.S. Patent as U.S. Pat. No. 3,949,335, issued to D. W. Morgan on Apr. 6, 1976, U.S. Pat. No. 4,866,010, issued to E. N. Boulos et al on Sep. 12, 1989, and U.S. Pat. No. 4,873,206, issued to J. V. Jones on Oct. 10, 1989. In addition, the present invention provides a unique high temperature melting glass with chemical characteristics similar to those high temperature melting glasses generally known in the art but with special chemical characteristics particularly adaptive to the sealing area in which such glass is destined to be employed.
Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein.